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Scan at 300 dpi in black and white, at actual size, with contrast high enough that pencil and light print read clearly. Color scans fax badly because fax is black and white only. A clean black-and-white scan usually faxes better than a photo of the same page.
| Setting | Use this | Why |
|---|---|---|
| Resolution | 300 dpi | High enough for small print; 600 dpi gains little since fax transmission caps detail |
| Color mode | Black and white (line art / text) | Fax sends only black and white; color adds gray noise without adding detail |
| Size | Actual size (100%) | Scaling down before faxing compounds with the fax's own scaling |
| Contrast | Raised for pencil or light print | Fax thresholding drops faint marks entirely |
| File format | PDF or TIFF | Both are accepted by nearly every online fax service |
A fax can only send black or white per dot. When you hand it a color scan, the software has to convert every shade into a pattern of black dots (halftone), which turns smooth backgrounds into speckled gray and can blur the edges of letters. Blue ink, yellow highlighter, and red stamps are the worst offenders: they photograph as mid-tones that fax as muddy gray smears. The fix is simple: scan in black-and-white mode, where the scanner decides "ink" or "paper" for each pixel instead of trying to preserve shades of gray.
This is the most common scan-to-fax failure. Fax machines use a brightness threshold: anything lighter than the cutoff becomes white paper, and pencil often falls below it. Three fixes work in order of effectiveness: raise the scanner's contrast setting so light marks darken before the fax ever sees them; if your scanner has a "text enhancement" or "remove background" mode, turn it on; and if the marks are still faint, trace over pencil signatures with a pen before scanning. Thermal receipts deserve special care: they fade, and scanning them hot out of the printer is never possible twice, so scan them the day you receive them.
Sometimes, but a scan is more reliable. Phone photos add three problems: page edges warp when the camera is not perfectly parallel, shadows darken one side of the page, and auto-focus can blur small type. If a scanner is not available, photograph the page in bright, even light from directly overhead, keep the whole page inside the frame, and convert the photo to black and white before faxing. For anything official (ID, signed forms, medical records), use a real scanner or a library scanner. A rejected fax because the signature was illegible costs more time than the scan saves.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
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